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Co-authored-by: OpenAI Codex <codex@openai.com> Signed-off-by: Alex Steiner <asteiner@nvidia.com>
…oe/fp8 APIs MiMo-V2.5-Pro-FP4 DFlash speculative decoding produced 0% draft acceptance (mean acceptance length = 1.0) whenever the runtime predated the num-blocks-first KV layout (vllm-project#42095): the draft read its KV cache through the wrong layout, so every drafted token was rejected. The target stayed correct (its KV was intact), which masked the issue as a draft-quality problem. On a runtime that includes vllm-project#42095, two stale APIs in the MiMo support blocked loading: - mxfp4.py: MiMoV2Mxfp4Config.get_quant_method checked isinstance(layer, FusedMoE), but the fused-MoE refactor turned FusedMoE into a factory function returning a MoERunner; the routed-expert module is now a RoutedExperts (matching the parent Mxfp4Config branch). Raised TypeError at model load. - fp8.py: restore a per-name get_cache_scale() shim. mimo_v2.load_weights still calls the per-weight form, which upstream renamed to get_cache_scale_mapper. Raised AttributeError at weight load. Also note: num_speculative_tokens must equal dflash block_size - 1. Validated on 8xB200 TP8 (built on base 3d300ae which includes vllm-project#42095): - short prompt: mean acceptance length 5.41, 63% draft acceptance - long prompt (3085 tokens, > SWA window): mean acceptance length ~2.3, ~20% acceptance, coherent output Previously 0% at all lengths. Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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June 12, 2026 02:10
Port of local-inference-lab/vllm divergence vllm-project#3: the DFlash reference uses HF output_hidden_states, where the entry after the final target layer is the POST-final-norm hidden state (all earlier entries are raw residual-stream values). MiMoV2Model captured the last aux feature pre-norm, degrading draft acceptance (long/hard-prompt mean accept length stuck ~2.0-2.3 vs official 3.18-6.30). Skip the last layer's pre-norm residual capture and append the normed hidden state after self.norm when the final layer id is an aux layer. Gated by VLLM_DFLASH_PRENORM_LAST_AUX=1 for A/B testing. On-node AL re-measure pending (node was unreachable at commit time). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Summary
Adds MiMo-V2.5-Pro-FP4 DFlash speculative decoding support and fixes an acceptance-length (AL) collapse.
Builds on the MiMo DFlash serving work (#45181) and base-model TP-sharding / FP4-MoE fixes (#45200). With those alone, DFlash produced 0% draft acceptance (mean accept length = 1.0) on the
v0.22.1runtime: that image predates the num-blocks-first KV layout (#42095), so the draft read its KV cache through the wrong layout and every drafted token was rejected. The target stayed correct (KV intact), disguising it as a draft-quality problem.On a runtime that includes #42095 (build on a base at/after
3d300aecb), two stale APIs blocked load:mxfp4.py—MiMoV2Mxfp4Config.get_quant_methodcheckedisinstance(layer, FusedMoE); the fused-MoE refactor madeFusedMoEa factory function and the routed-expert module aRoutedExperts.TypeErrorat load.fp8.py— restores a per-nameget_cache_scale()shim;mimo_v2.load_weightsstill calls the per-weight form (upstream renamed itget_cache_scale_mapper).AttributeErrorat weight load.Also:
num_speculative_tokensmust equal DFlashblock_size - 1.A later commit ports the post-final-norm last-aux-feature semantics from
local-inference-lab/vllm(gated byVLLM_DFLASH_PRENORM_LAST_AUX); see Notes.Validation (8×B200 TP8, built on a
#42095-inclusive base, runai_streamer load from NFS)Mean accept length by task type (temp 0), vs
local-inference-lab/vllmreference:Previously 0% at all configs. AL is task-type dependent (chat/long ≈ 2.5, code/math ≈ 4.4) and tracks the reference within ~0.5.
Notes for reviewers
#3post-norm last-aux commit is neutral on this FLASH_ATTN path. A same-node A/B (VLLM_DFLASH_PRENORM_LAST_AUXon/off) showed no AL change beyond noise — this branch already started above the reference's pre-fix ~2.0 (mask-embedding handled via [Spec Decode] Support mixed KV page sizes for DFlash #45181/Benjamin's qwen3_dflash). Kept because it matches reference semantics and is gated.MiMoV2Mxfp4MoEMethod.mimo_v2.py/fp8.py— needs reconciling (supersede or rebase) before merge.DFLASH_*_DEBUGlogging should be stripped before an upstream PR.How to run
Build from a
#42095-inclusive base; serve with--load-format runai_streamer(loads directly from NFS, no local staging) and--speculative-config '{"method":"dflash", ..., "num_speculative_tokens": <block_size-1>}'.